The layer-by-layer solar thermal fuel polymer film comprises three distinct layers (4 to 5 microns in thickness for each). Cross-linking after each layer enables building up films of tunable thickness.

While recent advances in solar technology have made the process of harvesting the sun’s energy less costly and more widespread than ever, Massachusetts Institute of Technology (MIT) researchers have developed a new way to farm and store solar heat, according to a university news release.

MIT professor Jeffrey Grossman, postdoctoral researcher David Zhitomirsky, and graduate student Eugene Cho say they have created a new type of polymer film that can soak up energy from the sun during the day and store it for a later release of heat.

This material could prove beneficial in a variety of circumstances, as heat from the sun is available only for, on average, less than half of the day worldwide. A new solar-based heating polymer could be an advantage in places with less sunlight or frequent cold.

Technology that converts the sun’s rays into heat or electricity is not a new development, but the material developed by the trio of researchers uses a new chemical process. While previous attempts at storing heat from the sun using similar solar thermal fuels were successful, they were only usable as liquid solutions and therefore not practical for many everyday needs. A solid polymer, however, could be more easily integrated into commonplace products or industrial processes.

The researchers’ new solar thermal fuels are designed using chemical compounds called azobenzenes that change on the molecular level in response to the sun’s energy, and are then capable of maintaining their charge indefinitely. A stimulus such as a small temperature burst causes them to revert to their original molecular layout, discharging the stored heat.

This process differs from past efforts to contain heat in solid objects using insulation, which, while somewhat effective, still leads to heat dispersion over time. Using the new polymer, the heat is stored as a chemical change rather than by itself, allowing all the energy to be trapped indefinitely until a release is chemically triggered. In its current state, the material is capable of releasing a warming blast of up to 50 degrees Fahrenheit across its surface, with researchers anticipating the potential to increase the temperature of the burst in the future.

The new polymer is the first solar thermal fuel to be solid-state, and was designed using common technology and production materials to maximize its future potential. The practicality of a thin, transparent film with solar energy storage capabilities may open the door for its application in a wide range of products.

The polymer could be woven into clothing to charge in daylight and instantly warm a wearer during the nighttime or cold hours. The material is also comparable in thickness to bonding polymers currently used in car windows, and could be installed in a similar way to quickly melt snow and ice from window glass.

The MIT team will continue work on the film as they try to improve its capacity and color, but its release in the future could signal a big step for heating operations.

“The approach is innovative and distinctive,” said Ted Sargent, a professor and the vice-dean for research at the University of Toronto, in the MIT release. “The research is a major advance towards the practical application of solid-state energy-storage/heat-release materials from both a scientific and engineering point of view.”